It is well-recognized that stress can adversely affect health. It is unclear, however, what factors in this complex relationship predict poor health outcome. Specific qualities of the stressors (e.g., undesirability) are clearly important. In addition, personality traits, social support, and other personal characteristics seem to play a mediating role in the effect or stress on health. Suppression of immune function has been demonstrated in a variety of populations, including bereaved persons and academically-stressed students. This may be one mechanism by which stress can increase one's vulnerability to disease. This study will examine the relationship between stressful life events and immune response to a novel antigen (primary immune response). The questions to be answered are: (1) how does stress affect the primary immune response? (2) how do level of stress and personal-social characteristics interact to affect primaryimmune response? The hypotheses are that the more stressed subjects will have a diminished immune response to the immunizing antigen, and that psychosocial factors can modify the suppressive effect of stress on the immune system. Subjects (healthy, 18-24 year old female students) will complete questionnaires to obtain the following: (1) sociodemographics, health history, health habits (2) level of stress experienced--both discrete "major" and day-to-day "minor" life events (3) potential psychosocial mediators of stress: state of psychological distress/well-being, locus of control, and social support. Subjects will then be immunized with Keyhole limpet hemocyanin (KLH), a benign complex protein frequently used in studying primaryimmune response. Outcome will be measured by serum anti-KLH antibody titers and in vitro KLH-induced lymphocyte stimulation studies at 3 and 8 weeks post immunization. Data analysis will include calculation of correlation coefficients between scores on the stress measures and (1) immune response at 3 and 8 weeks and (2) the difference between post- and pre- immunization values. We will also use multiple regression to analyze the relative contributions of stressful events and psychosocial mediators to primary immune response. Causal models will be tested using path analysis.